1. Field of the Invention
The present invention relates to a fluid regulator thermostat, in particular for a cooling fluid of an internal combustion engine, and also to a method of fabricating such a thermostat.
The invention relates more particularly to thermostats that combine firstly a thermostatic element that is responsive to the temperature of the fluid to be regulated, controlling the shutting of a flow of fluid through the thermostat and associated with a return spring, and secondly a body within which there are arranged both said thermostatic element and the spring. The body of the thermostat must satisfy conflicting constraints: firstly the structure must be sufficiently rigid to absorb the pressure of the fluid being regulated and the mechanical forces associated with operation of the thermostatic element and its return spring, and secondly the structure must be sufficiently open to define one or more paths for allowing the fluid to pass through the thermostat, and at satisfactory flow rates.
2. Brief Description of the Related Art
Traditionally, the body of this type of thermostat is molded out of a plastics material for numerous reasons, in particular ease and cost of fabrication. Nevertheless, the use of a plastics material involves significant design constraints associated with the only moderate mechanical strength of the plastics material, in particular in terms of resistance to creep: within a cooling circuit for an internal combustion engine, the body of the thermostat is subjected to vibration, and at certain engine speeds, the temperature of the cooling fluid can reach values that are high. Taking these mechanical and thermal constraints into account requires the thermostat body, when made of plastics material, to be dimensioned with walls of significant thickness, thereby limiting the maximum flow rate possible through the thermostat.
To avoid that drawback in part, proposals have been made in the past to reinforce the structure of the plastics material body with one or more metal pieces fitted thereto. In particular, a metal washer is sometimes provided in the zone of the thermostat body that absorbs the reaction from the return spring of the thermostatic element. Nevertheless, recourse to fitting such metal pieces not only complicates the design of the thermostat body, thereby limiting options for installing the thermostat at various points within a cooling circuit and/or within different circuits, but also complicates the fabrication of the thermostat since it requires a large number of parts to be assembled.
In the past, proposals have also been made to integrate the thermostat within a body made of two distinct parts of plastics material that are of generally tubular shape, and that are for fitting to each other with an interposed sealing gasket. That body forms a kind of housing that presents a major risk of leaking, and it generally incorporates an internal reinforcing metal bracket for absorbing the forces associated with the work of the thermostatic element, thereby likewise complicating the design of the thermostat and its fabrication.
U.S. Pat. Nos. 3,351,279 and 3,792,813 propose using a thermostat body that is made entirely out of metal, thereby ensuring good mechanical strength. Nevertheless, such metal bodies raise fabrication problems and problems of assembly with the other components of the thermostat, in particular the thermostatic element and its return spring.
Thus, U.S. Pat. No. 3,351,279 proposes a thermostat body in which one of the spring support arms is not formed integrally with the remainder of the body, but is fitted to the body either by means of a hinge or by wedging. Fabrication of the body is thus complex, and in operation the connection zone between the fitted arm and the remainder of the body presents a risk of breaking or of malfunctioning.
U.S. Pat. No. 3,792,813 also envisages various metal embodiments for thermostat bodies, each made up of two distinct portions that are fitted together. In its FIG. 7, that document discloses a one-piece embodiment, in which two arms for supporting a spring of a thermostatic element are made integrally out of the same material as the remainder of the thermostat body, which body can be made by stamping. Nevertheless, although U.S. Pat. No. 3,792,813 explains how the thermostat is to be assembled when the body is made of two parts, specifically by taking advantage of its two-part structure for assembling the thermostatic element and its spring in one of the parts of the body prior to fastening the other part thereto, that document is silent as to how to assemble the one-piece body with the other components of the thermostat. Thus, the one-piece solution proposed in U.S. Pat. No. 3,792,813 cannot be made in practice, it being observed in addition that the arms of the thermostat body are inclined at 45° relative to the working axis of the thermostatic element and of its spring, such that, in operation, those arms run the risk of splaying apart from each other under the action of the forces generated by the thermostatic element and the spring, thereby leading to malfunction of the thermostat.